1. Field of the Invention
This invention relates to agent feeders and in particular to those feeders adapted for use with pipe casting apparatus.
2. Description of the Prior Art
The production of cast iron and ductile iron pipe by a DeLavaud system incorporating permanent or semipermanent metal molds and utilizing a centrifugal casting procedure, is well known in the art. Illustrative of such a system is the centrifugal casting apparatus as shown in U.S. Pat. No. 1,949,433, wherein there is described a pouring ladle for receiving the molten metal, such as iron, and for accurately pouring a predetermined amount of the molten metal within a predetermined length of time, into a fixed trough positioned on an incline to carry the molten metal to the metal mold contained within and rotated by a casting machine. Further, the casting machine is mounted on wheels to move along a track in a rectilinear motion, whereby the fixed trough may be inserted into and withdrawn from an opening within the casting machine. As shown in the U.S. Pat. No. 1,949,433, the casting machine includes a rotating, water-cooled metal mold for receiving the molten metal discharged from the end of the trough, as the casting machine is moved with respect to the trough's discharge end. Such casting machines are very complex and closely controlled through the use of timers, limit switches and pre-programmed pouring cycles.
Typically, the method of pouring a single pipe includes the following steps. First, the casting machine is moved along its track to a position whereat the fixed trough is fully inserted within the water-cooled metal mold and its metal mold is rotating at a predetermined speed. Next, the machine ladle is activated whereby it is lifted so that molten metal is discharged into the trough at a predetermined flow rate. A time delay is permitted in which the molten metal fills the trough and then, the casting machine is activated so that it moves at a predetermined rate until the fixed trough is removed from its opening. As the trough is drawn through the casting machine, the molten metal is discharged along the length of the metal mold as it is rotated, whereby a uniform thickness of the molten metal is deposited upon the interior surface thereof. The pouring rate and the travel rate of the casting machine determines the thickness of the resultant pipe cast. After the metal has solidified, the pipe is extracted from the mold, and the casting cycle, as described above, may be repeated.
Use of various agents within the casting process to effect the structure of the cast pipe is known. In particular, it is well known that the microstructure of cast iron and ductile iron (carbides, peralite, ferrite, etc.) is affected by the following factors: (1) its chemical content (for example, various agents such as C, Si, Mn, Mg, Cr. etc, may be added); (2) the cooling rate: and (3) the nucleating agents present. It is apparent that the addition of various chemical substances into the molten metal will produce various alloys determined by the intended use of the cast pipe. Further, the addition of nucleating agents prior to the casting of a pipe can produce dramatic changes in the as-cast structure of the pipe. For example, nucleating or inoculating alloys or agents such as Ferro-silicon, Calcium-silicon or graphite may be added to the molten cast iron at various points in its casting process. The inoculating agent can be added to the molten metal within the machine ladle, to the molten metal as it is poured from the machine ladle into the trough, or into the molten metal as it leaves the discharge end of the trough and before it is disposed upon the interior surface of the rotating metal mold. Alternatively, as shown in the above-noted U.S. Pat. No. 1,949,433, the inoculating or nucleating agent can be distributed over the inner surface of the rotating metal mold before the metal is poured, which process permits the inoculating agent to be dissolved in the molten metal and also to serve as an insulator between the molten metal and the relatively cold suface of the metal mold, whereby the processing time required for the molten metal to freeze is increased.
It is important to closely control the amount of the inoculating or nucleating agent. Typically, the amount of material used is in the order of 0.1% to 0.2% of the weight of the pipe cast. For example, for a 20 foot long 6-inch diameter pipe, the amount of the agent distributed over the mold surface would be in the order of 0.6 lb. to 1.2 total, or 0.015 lb. to .030 lb. per square foot of mold surface. A uniform distribution over the mold surface is absolutely required. If the distribution is uneven and a space of the mold receives insufficient or no inoculating material, the molded pipe may crack, and if too much agent is deposited, surface defects of sufficient magnitude may result to scrap the pipe.
A modern DeLavaud pipe casting machine can produce pipes at rates of 60-pipes-per-hour or greater, which means that the use of the inoculating agent must be essentially automatic as well as reliable. To keep up with production demands, various schemes have been attempted to achieve the rapid as well as substantially uniform distribution of the inoculating or nucleating agents onto the pipe mold. For example, in one known scheme the powdered inoculating or nucleating agent is placed in a second through (not to be confused with the first-mentioned trough for the molten metal), to be inserted along the full length of the molten metal trough and prior to the deposition of the molten metal onto the interior surface of the metal mold, tilting the second trough while the mold is rotating, whereby a substantially uniform distribution of the agent is achieved over the length of the metal mold. A variation of this technique is set out in U.S. Pat. No. 1,963,147 wherein a second trough for the powdered agent is provided in combination with a pipe having a plurality of jets formed along the length of the second trough to assist the feeding of the powdered agent to the metal mold. Both of these arrangements, require that the second trough be separately filled, thus effectively preventing the incorporation of such a method into an integrated, automatic pipe casting machine.
A further type of apparatus for feeding inoculant to the surface of a metal mold is shown in the afore-mentioned U.S. Pat. No. 1,949,433, whereby the powdered agent is fed at a measured rate into a suitable receptacle such as a funnel. The funnel is conventionally open to the atmosphere, but may be screened if desired to prevent contamination. The granular inoculating or nucleating agent is thus directed into a cylindrical passage wherein the agent is subjected to a relatively high veocity of air or gas by a venturi nozzle and is thereby conveyed through a conduit to the molten metal trough. The use of such an arrangement has several distinct disadvantages. First, very large quantities of compressed air or gas are required to convey the desired amount of agent to the end of the trough. Such a large quantity of air passing through the relatively small diameter of the jet results in high discharge velocities, which prevent uniform distribution of the agent over the surface of the metal mold and may result in displacement of particulate matter and/or molten metal from the mold surface. In addition, the high gas velocities cause extreme abrasion and/or corrosion problems of the conveying equipment as well as the metal mold. This abrasion problem is particularly significant in that the agents are typically very hard alloys, which, in powder form, are very abrasive. Further, the tube which delivers the inoculating or nucleating agent to the end of the molten metal trough is closed off at its end and has a series of small openings adjacent the closed end through which the agents must pass to reach the surface of the metal mold. The use of high-velocity gases to deliver the agent can result in excessive turbulence and/or build-up of powdery agent material which eventually causes these small openings to be plugged up. This results in an increase in back pressure making controlled agent delivery difficult, if not impossible. High velocity agent feeders are not in themselves easily controllable as to the rate at which the agents are fed to the mold surface and apparatus subject to back pressure variations in the delivery tube only adds to the problems of the manufacturing process.
A further type of agent feeder is shown in U.S. Pat. No. 1,963,148 wherein a pipe having a plurality of openings serves to introduce a relatively high velocity of gas into a mixing chamber into which a measured quantity of the agent is also introduced. A fine powder mixture of the high-velocity gas and the agent is formed and directed via a conduit having one end extending into the mixing chamber. A plurality of openings are provided along the length of the conduit and the conduit extends along the entire length of the molten metal mold whereby the fine powder mixture, under pressure, is directed at one time through the openings and onto the mold surface. This conduit is fixed in its relationship with the metal trough and is not withdrawable. The primary difficulties with such an agent feeding mechanism is that the rate of agent deposition is limited and that it is difficult to secure uniform disposition along the entire length of the pipe, due to the agent material settling out of the fine powder mixture. Further, the openings are subject to frequent plugging resulting in non-uniform application of the agents onto the mold.